It is known that a certain amount of entrained air can improve the durability of concrete, a brittle material, by increasing resistance to degradation arising from freeze-thaw cycling. The nature and extent of air entrainment in concrete must be carefully controlled, however, because excessively large or unevenly spaced air voids can lead to loss of freeze-thaw durability and compressive strength. Air entraining agents, such as rosins acid and anionic surfactants, are commonly used to control the size and spacing of air voids within the cementitious mix.
Water-reducing cement dispersing admixtures, particularly so-called “superplasticizers,” are known to entrain excessive air in concrete slurries. Air detrainers (“defoamers”) are used to correct this problem.
Defoamers with high hydrophobicity have limited solubility in water and are not easily incorporated into aqueous solutions, which, for the most part, comprise the water-reducing admixture compositions. This hydrophobicity tends to destabilize the aqueous product and fosters separation of components. It requires that the water-reducing cement dispersant and defoamer be constantly stirred to prevent separation, or that they be stored in separate tanks and mixed just before use.
In view of the above, new compositions and methods for incorporating defoamers and cement dispersing water-reducers are needed in the cement and concrete industries.